U.S. application Ser. No. 09/927,151 of Alan C. Nelson, filed Aug. 10, 2001, now U.S. Pat. No. 6,522,775 issued Feb. 18, 2003, entitled “APPARATUS AND METHOD FOR IMAGING SMALL OBJECTS IN A FLOW STREAM USING OPTICAL TOMOGRAPHY,” (hereinafter called the FOT design) is incorporated herein by this reference. In the aforesaid Nelson patent application, cell motion is accomplished in a flow stream, wherein cells in suspension move with constant velocity along the single flow axis of a capillary tube. The FOT design does not address the more general case where cell velocity and/or direction of motion are variable.